Lung cancer is the leading cause of cancer death. Therefore, new strategies in the treatment of lung cancer are being explored. One promising approach has been immunotherapy. A better understanding of the interaction between inflammatory, tumor cells and the lung microenvironment will open new perspectives to boost the efficacy of current immunotherapy. Tumor-associated neutrophils (TANs) represent a significant portion of inflammatory cells within the lung tumor microenvironment; however, the role of TANs and their subsets in cancer progression remains largely unexplored in human. We provided evidence that instead of being immunosuppressive, as most mouse models suggested, TANs are able to stimulate T cell responses in early stage human lung cancers. Thus, TANs demonstrated one of the most important characteristics of anti- tumoral N1-like neutrophils. In addition, we discovered a novel subset of TANs that forms the basis of this proposal. We found that the majority of TANs express classic neutrophil markers (canonical TANs). However, in addition, we identified subpopulation of TANs that displayed a unique combination of neutrophil (Arg1+MPO+CD66b+CD15+) and antigen-presenting cell (CD14+HLA-DR+CCR7+CD86+) markers (hybrid TANs). These hybrid TANs comprised 0.5-25% of all TANs. Using human bone marrow (BM) cells, we identified conditions in which immature granulocytes could be differentiated into cells that highly resemble hybrid TANs. The BM and tumor-derived hybrid TANs differ from canonical TANs by: 1) increased expression of T cell co-stimulatory molecules and Fc? receptors, 2) augmented ability to stimulate the T cell response, and 3) increased ability to cross present viral antigens. Based on these preliminary data, we hypothesize that this newly identified subset of TANs has the potential to mediate key anti-tumor immune functions in early stage lung tumors, such as antibody-dependent tumor cell mediated cytotoxicity (ADCC) and the stimulation of tumor-specific T cell responses. To test this hypothesis, we will investigate the mechanisms of augmentation of the effector phase of T cell responses by hybrid cells (Aim 1.1) as well as the ability of hybrid neutrophils to cross present tumor antigens to cytotoxic CD8 cells (Aim 1.2). We will identify the progenitors of hybrid neutrophils (Aim 2.1), along with the transcription factors (Aim 2.2) responsible for the formation of these cells. We will determine the mechanisms of hybrid neutrophil-mediated ADCC (Aim 3.1) and the clinical potential of hybrid neutrophils to mediate ADCC (Aim 3.2). Finally, we will elucidate the prognostic impact of hybrid TANs (Aim 4). The goal of this proposal is to determine the specific roles of this unique subset of TANs in regulation of tumor development in early stage lung cancer patients and to develop novel approaches to boost anti-tumor immunity by engaging the hybrid neutrophils. The successful completion of this study will generate new knowledge about the unique subset of human TANs that will be important in prognostication and designing new therapeutic strategies. Therefore, this work will have important translational ramifications.